The coexistence of a picture tube and an audio reproduction device in the same housing can lead to visual and audible problems when the audio output power increases and if there is tight mechanical coupling between the picture tube and parts vibrating in response to the electrical audio power.
One of these mentioned problems is audible buzz. The buzzing sound is in most cases created by vibration of the shadow mask or of the shadow mask frame when the audio output level is high and when the momentary audio frequency is at or near the self-resonant frequency of the shadow mask or the mask/frame arrangement.
Another problem is the unwanted modulation of the electron beam intensity due to the vibration of the shadow mask or its components caused by insufficient mechanical decoupling from the sound reproduction equipment as described above. This leads to brightness variations and/or colour purity imperfections appearing in synchronism with the momentary audio frequency. It is obvious that this mentioned problem is worse at or near the self-resonant frequency of the mask or the mask/frame arrangement.
Unfortunately, this second problem is further increased when for a high resolution monitor a picture tube with a fine pitch is selected because the same vibration amplitude of shadow mask components, e.g. wires in case of a Trinitron.RTM. type, causes a larger relative landing error on the screen.